The S100 human proteins (S100A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, S100B, S100P, S100Z) are a large family of cytoplasmic and extracellular Ca2+-binding proteins characterized by a high degree of conservation in amino acid sequence and 3-D structure [Zimmer, Sadosky and Weber (2003), Microsc Res Tech 60(6): 552-9]. They are small, acidic proteins of 10-12 kDa and contain two distinct EF-hands. A modified, S100-specific EF-hand is located at the N-terminus, followed by a classical Ca2+-binding EF-hand.
Neoplasias are the most numerous human diseases in which dramatic changes in the expression of S100 proteins occur. Over expression of S100A4, S100A6, S100A7, S100A11, S100A14, S100A16, S100B, S100P, or S100Z is common in many cancers of different origin (breast, colon, lung, pancreas, and others). At least partially such changes might be caused by rearrangements (amplifications) in chromosomal region 1q21, where most of S100 genes are clustered. Such rearrangements are frequently observed in different tumor cells.
Out of all S100 proteins the role for S100A4 in invasive growth and metastasis of cancers is especially well documented. Properties of this protein were recently reviewed in Helfman, Kim, et al. (2005) Br J Cancer 92(11):1955-8 and Mazzuchelli (2002) Am J Pathol 160(1): 7-13. Transfection experiments showed that S100A4 can induce a metastatic phenotype in previously non-metastatic rat mammary cells [Lloyd, Platt-Higgins, et al. (1998). Oncogene 17(4): 465-73], B16 murine melanoma cells [Parker, Whittaker, et al. (1994) DNA Cell Biol 13(10): 1021-8] and human breast cancer MCF-7 cells [Ambartsumian, Klingelhofer, et al. (2001) Oncogene 20(34): 4685-95]. Conversely, antisense S100A4 RNA or anti-S100A4 ribozyme suppressed the metastatic potential of highly metastatic cell lines [Maelandsmo, Hovig et al. (1996) Cancer Res 56(23): 5490-8 and Takenaga, Nakamura et al. (1997) J Cell Biol 124(5): 757-68]. The important role of S100A4 in tumor malignisation was demonstrated in transgenic mouse studies. It was shown that S100A4 by itself was not able to initiate tumors but it induced metastatic disease in originally non-metastatic tumors initiated by other oncogenes [Ambartsumian, Grigorian et al. (1996); Oncogene 13(8): 162 1-3 and Davies, Rudland et al. (1996); Oncogene 13(8): 1631-7]. When dynamics of tumor development were studied in S100A4 knock-out mice a significant delay in tumor uptake and decreased tumor incidences were observed. Moreover, tumors developed in S100A4(−/−) mice did not metastasize. Immunohistochemical analyses of these tumors revealed reduced vascularity and abnormal distribution of host-derived stroma cells. Coinjection of S100A4(+/+) fibroblasts partially restored the dynamics of tumor development and the ability to form metastasis, underlying the determinative role of host-derived S100A4-positive stroma cells in tumor progression and metastasis [Grum-Schwensen, Klingelhofer, et al. (2005) Cancer Res 65(9): 3772-80]. Altogether these observations suggest that S100A4 is not simply a marker for metastatic disease, but rather has a causal role in mediating this process.
The association between S100A4 expression and metastasis observed in animal studies has led to a number of studies examining the utility of S100A4 expression as a prognostic marker in human cancers. Two retrospective studies, based on the same well characterized group of 349 patients with a follow-up period of 19 years [Platt-Higgins, Renshaw, et al. (2000) Tnt J Cancer 89(2): 198-208; and Rudland, Platt-Higgins, et al. (2000), Cancer Res 60(6): 1595-603] analyzed the prognostic significance of protein S 100A4 in breast cancer and evaluated the association between protein expression, as detected by immunohistochemical staining, and variables with potential prognostic value for patient outcome. The antiserum stained 56% of the carcinomas either strongly or at a borderline level, whereas 44% of the carcinomas remained unstained. The overall survival for patients with carcinomas expressing S 100A4 was significantly worse than for those patients considered negative for S 100A4. In analogous studies the prognostic significance of protein S100A4 expression has recently been evaluated in a series of esophageal-squamous carcinomas, non-small lung cancers, and primary gastric cancers [Kimura, Endo et al. (2000) Tnt J Oncol 16(6): 1125-31; Yonemura, Bndou, et al. (2000) Clin Cancer Res 6(11): 4234-42; and Ninomiya, Ohta, et al. (2001) mt J Onco 18(4): 715-20]. Patients with S100A4-positive esophageal carcinomas [of 52 (25%)] had a significantly poorer prognosis than patients with S100A4-negative carcinomas; the protein S100A4 status in cancer specimens remained the only independent prognostic parameter in a multivariate analysis. Immunohistochemically S100A4 was detectable in 81 of 135 (60%) lung cancers. S 100A4 was found to be useful to identify patients with poor prognosis, as its tissue expression was correlated with progression of the tumor size as well as nodal status. Finally, protein S 100A4 was found to be significantly more expressed in poorly than in well-differentiated gastric adenocarcinomas [of 92 (55%)], and was correlated with nodal metastatic disease and peritoneal dissemination. Immunohistochemical studies revealed no staining for protein S 100A4 in the epithelial cells of normal colonic mucosa and in colonic adenomas, whereas carcinomas arising in adenomas and invasive carcinomas showed S100A4 expressing cells in 44% [of 18] and 94% [of 53] of cases, respectively (Takenaga, K., Y. Nakanishi et al. 1997). In pancreatic cancer, no S100A4 expression was found in low-grade intraepithelial neoplasia lesions [of 69], low level of expression was detected in high-grade pancreatic neoplasia lesions [of 18 (17%)], but most of pancreatic invasive carcinomas expressed S100A4 [of 61(93%)], see Rosty, Ueki et al. (2002) Am J Pathol 160(1): 45-50. Expression of S 100A4 was also associated with metastasis and poor survival in patients with bladder cancer [Davies, B. R., M. O'Donnell, et al. (2002) J Pathol 196(3): 292-9]. Altogether these results unequivocally demonstrate the importance of S100A4 protein expression for cancer progression, especially in the invasive stage.